1. Field of the Invention
This invention relates to improvements in an engine muffler for a small-sized engine, for example, of a brush cutter or a chain saw.
2. Description of the Related Art
As shown in FIG. 7, a conventional muffler used for a small-sized engine comprises a first expansion chamber 2 for exhaust gas which includes an exhaust gas inlet 1 to be connected to an exhaust port of the engine, a second expansion chamber 4 which includes an exhaust gas outlet 3, and an exhaust gas purifier 5 disposed between the first expansion chamber 2 and the second expansion chamber 4 in which a catalyst for purifying exhaust gas is coated on a stainless-steel base body including many pores, for example, a honeycomb stainless-steel base body.
In such an engine muffler containing an exhaust gas purifier, as already known, the distance between an exhaust gas inlet and the exhaust gas purifier of a first expansion chamber is designed to be shorter, so that an unburnt gas is completely combusted in the first expansion chamber heated by exhaust gas, and thus substances such as carbon monoxide and nitrogen oxides contained in exhaust gas are decreased.
However, in an engine muffler used for a small-sized engine, the distance between an exhaust gas inlet and an exhaust gas purifier is extremely difficult to make longer.
With regard to the conventional muffler shown in FIG. 7, in order to make as long as possible the distance between the exhaust gas inlet 1 and the exhaust gas purifier 5, and the distance between the exhaust gas purifier 5 and the exhaust gas outlet 3 and also make it compact, the muffler is constructed such that the exhaust gas which has entered at the exhaust gas inlet 1 disposed in the upper part of the first expansion chamber 2, passes through the exhaust gas purifier 5 disposed in the lower part of the adjoining first expansion chamber 2 and second expansion chamber 4, and then is discharged from the exhaust gas outlet 3 disposed in the upper part of the second expansion chamber 4. In the muffler according to this construction, the distance between the exhaust gas inlet 1 of the first expansion chamber 2 and the exhaust gas purifier 5 and the distance between the exhaust gas purifier 5 and the exhaust gas outlet 3 of the second expansion chamber 4 are designed to be as long as possible. However, the intended effect of purifying exhaust gas could not be sufficiently produced.
For the purpose of solving this problem, as shown in FIG. 8, a muffler has been developed which comprises a first expansion chamber 2 for exhaust gas which includes an exhaust gas inlet 1 to be connected to an exhaust port of an engine, a second expansion chamber 4 which includes an exhaust gas outlet 3, a concave exhaust gas receiving member 6 which has a plurality of vent holes 6b passing through a concave surface 6a thereof, the exhaust gas receiving member 6 being disposed in the first expansion chamber 2 such that the concave surface 6a faces the exhaust gas inlet 1, and an exhaust gas purifier 5 in which a catalyst for purifying exhaust gas is coated on a stainless-steel base body including many pores, for example, a honeycomb stainless-steel base body, the exhaust gas purifier 5 being disposed between the first expansion chamber 2 and the second expansion chamber 4.
In the conventional improved muffler shown in FIG. 8, the concave exhaust gas receiving member 6 which has the plurality of vent holes 6b passing through the concave surface 6a is disposed in the first expansion chamber 2 such that the concave surface 6a faces the exhaust gas inlet 1, so that the concave exhaust gas receiving member 6 produces the effect of noise reduction. In addition, the complete combustion of unburnt gas is conducted by the heat of the concave exhaust gas receiving member 6 which has been heated by exhaust gas, so that the emission of harmful gases such as carbon monoxide and nitrogen oxides contained in exhaust gas can be decreased. However, even in the muffler according to this construction, the intended effect of purifying exhaust gas of harmful substances could not be sufficiently produced.